Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

398
FXUS63 KLOT 280752
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
252 AM CDT Sun Jun 28 2026

.KEY MESSAGES...

- A decaying cluster of thunderstorms may affect portions of
  northern Illinois this afternoon.

- Dangerous heat is expected across the area this week.

- Afternoon heat index values forecasted over 100 degrees each
  day next week, with little to no relief at the lakeshore and
  at night.

&&

.DISCUSSION...
Issued at 252 AM CDT Sun Jun 28 2026

A weak 925-850 hPa warm front stretching WNW to ESE from around
Lee County to just south of the Kankakee River Valley in
northwest Indiana continues to provide a focus for spotty light
showers early this morning. Meanwhile, a developing surface
theta-e gradient associated with notably higher moisture just
southwest of the CWA will lift northward through the day. Weak
low-level isentropic ascent associated with these features
should allow for an axis of increased cloud cover and perhaps a
few light showers/sprinkles late this morning into this
afternoon.

Severe convection tracking along and north of the SD/NE line
early this morning will remain the primary focus for the
forecast area this afternoon. This cluster of convection has
remained fairly strong through much of the night, with an
associated MCV now evident. Renewed convective cells over
northeast Nebraska ahead of this complex indicate that the
environment is not entirely capped farther south. The convection
will begin to encounter substantial low to mid-level warming
with an incoming EML lifting northeast across the Mississippi
River Valley late this morning into the afternoon. However, the
combination of steepening mid-level lapse rates, low-level
moisture advection, and local weakening of capping near any
mature MCV does warrant some concern for convection to persist
across the Mississippi River and into the CWA. With modestly
strong mid-level flow across southern Wisconsin and a strong
instability gradient bifurcating the CWA, there is a sweet spot
where convection, possibly severe, could event remain well
formed and track well into (or even across) the CWA. Have
introduced chance PoPs for showers and storms west of the
Chicago metro, and slight chance PoPs elsewhere, for the
afternoon. Additionally, some CAMs indicate that any decaying
MCV could produce a wake low and resultant stronger southeast
winds over portions of the area this afternoon.

Regardless of potential convection, heat and humidity will
begin to build today with heat index values rising to around 90
inland during the afternoon and persistent onshore flow
maintaining cooler conditions along the shore.

The well-advertised period of heat this week remains on track,
particularly Monday through Wednesday. An anomalously strong
mid-level ridge (heights very near 600dam) drifting along the
Ohio River Valley and H850/H700 temps of over 25C/12C Monday
through Wednesday will yield unseasonably warm conditions with
daytime highs well into the 90s while building an incredibly
strong cap over the local area. Combined with persistent
southwest low-level flow, there looks to be no relief from lake
breezes or upstream convective outflow boundaries during this
time. Though capping will be quite strong for Monday and Tuesday
(and possibly into Wednesday), persistent strong southwesterly
gradient flow will likely allow for modest mixing into
incredibly dry air across the base of the EML. Though this may
lower dew points by just a couple degrees (e.g. mid 70s vs upper
70s), the difference may be enough to keep heat index values in
check.

Have maintained the Extreme Heat Watch for Cook County from
Monday through Wednesday, and issued a Heat Advisory for the
remainder of the forecast area for the same period. Expectations
are that Cook County will need to be upgraded to an Extreme
Heat Warning (criteria of heat index values of 100 or higher for
three days). Outside of Cook County, this looks like a solid
long duration advisory event with afternoon heat index values
hovering around 105 degrees (Heat Advisory criteria). A case can
be made that the longevity of the heat may require an eventual
upgrade to an Extreme Heat Warning for areas outside of Cook
County if convection remains north of the area on Thursday and
Friday.

Regarding the potential for convection this week, the strong
cap early in the week should deflect convection well to the
northwest (Minnesota through Upper Michigan) through at least
Wednesday. An expected flattening of the ridge and eventual SW
to NE orientation of the ridge axis toward the western Great
Lakes would favor increasing chances for convective episodes to
affect some or all of the forecast area as early as Wednesday
night. And with guidance often too slow with breaking down the
periphery of summertime ridges in the Great Lakes, direct or
indirect (outflow) impacts from convection lowers confidence on
headlines beyond Wednesday. The overall message is for heat to
potentially persist into the Independence Day holiday, but for
increasing chance for convection with each day.

Kluber

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 101 AM CDT Sun Jun 28 2026

Aviation concerns for the 06Z TAFs:

- Patchy MVFR ceilings possible this morning for a time after
  sunrise.

- Low chance (20-30%) of a period of SHRA/TSRA this afternoon
  with highest chances at KRFD after ~19Z.

Early morning surface analysis depicts seasonably deep low
pressure centered over the far northeast CO/NE border, with a
largely stationary frontal boundary stretching east-
southeastward across the lower MO Valley into southern IL/IN.
A relatively moist low-level air mass remains in place north of
this front into northern IL/IN which continues to support areas
of lower-end VFR clouds across the terminals, though some larger
breaks have developed in spots. Expectation is that at least a
patchy 4-7 kft deck will linger through the remainder of the
overnight hours, with redevelopment of diurnal cu/stratocu
after sunrise. Given the small temp-dew point depressions this
may initially develop as an MVFR deck this morning, before
gradually rising to 3500-4000 ft by afternoon.

Concern then turns to a thunderstorm complex currently tracking
east-southeastward across NE/SD at issuance time, and guidance
trends that suggest that the southern portion may spread into
portions of northern IL at least in a weakening fashion this
afternoon on the nose of a low- level jet and steep mid-level
lapse rate plume. Current high-res CAM guidance supports the
greatest potential (~30%) for TSRA at KRFD and have added a
prob30 there in the 19-21Z time frame. Indications of further
weakening and a decreasing footprint farther east into the
Chicago terminals support a prob30 for SHRA, though we`ll have
to monitor convective trends later today in case TS chances
increase there.

Wind wise, light northeast winds will turn east-southeast around
10 kt after sunrise, and persist through much of the period.
Gusts 20-25 kts appear most likely at KRFD where the gradient
will be tightening along/west of the MS Valley in response to
the low lifting across the Plains. Did include a gust mention
in the SHRA prob30 for the Chicago terminals however. Surface
winds do look to eventually veer south or south-southwest toward
Sunrise Monday morning, as the stationary front to our south
eventually lifts across the area as a warm front.

Ratzer

&&

.CLIMATE...
Issued at 252 AM CDT Sun Jun 28 2026

     .Daily Records for the Upcoming Week........

Chicago (KORD)
            Record High       Record Warm Minimum
June 29       97 (1954)            80 (1931)
June 30       99 (1953)            80 (2018)
July 1       103 (1956)            78 (1931)
July 2        99 (1970)            79 (1911)
July 3       102 (1949)            78 (1911)
July 4       102 (2012)            80 (1921)


Rockford (KRFD)
            Record High       Record Warm Minimum
June 29      103 (1931)            75 (1931)
June 30      102 (1931)            76 (2018)
July 1       101 (1931)            76 (1970)
July 2        99 (1910)            74 (1970)
July 3        99 (1925)            75 (2012)
July 4       102 (2012)            77 (1977)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory from noon Monday to 10 PM CDT Wednesday for
     ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ106-ILZ107-ILZ108.

     Extreme Heat Watch from Monday afternoon through Wednesday
     evening for ILZ103-ILZ104-ILZ105.

IN...Heat Advisory from noon CDT /1 PM EDT/ Monday to 10 PM CDT /11
     PM EDT/ Wednesday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

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